Several techniques are available to process materials, including single screw extruders, twin screw extruders and batch mixers. Single screw extrusion is typically used for core operations in polymer processing. A goal of a single screw extrusion process is to build pressure in a polymer melt so that it can be extruded through a die or injected into a mold. Twin screw extrusion, on the other hand, is used extensively for mixing, compounding, reacting and extruding materials. For example, twin screw extruders can be used for processing many types of polymeric materials; although other materials can also be processed with twin screw extruders such as raw materials for food processing.
In operation, twin screw extruders have a profile for extrusion of thermally sensitive materials (e.g., PVC) and specialty polymer processing operations, such as compounding, devolatilization, chemical reactions, etc. Also, twin screw extruders exhibit improved processing capabilities. For example, twin screw extruders can have intermeshing or non-intermeshing screws along each of their entire length and throughout the housing, and can be designed as co-rotating or counter-rotating to achieve particular mixing characteristics. In this way, using intermeshing screws, the twin screw extruders can offer improved feeding and more positive conveying characteristics, which allow the machine to process hard-to-feed materials (e.g., powders, slippery materials, etc.). The twin screw extruders also yield short residence times and a narrow residence time distribution (RTD). Also, the twin screw extruders exhibit improved mixing, with larger heat transfer areas to allow improved control of stock temperatures.